Is a straight woman more at risk of getting hiv via vaginal unprotected sex than a straight man?

Yes and no: HIV is more efficiently transmitted by vaginal sex from male to female than F to M, roughly twice as often for any single exposure. That suggests women are at higher risk. OTOH more men are likely to have multiple partners and exposures than women. From that standpoint, men are at higher risk. On balance, it's about equal. For most heterosexual singles in US, sexually transmitted HIV remains rare.

HIV transmission ris: From penile vaginal intercourse one has to have a + partner who is not protecting him/herself. Also condoms occasionally break or slip off. Spermicides help!